Process for preparing a photosensitive element and process of using same in a diffusion transfer method



y 3, 1966 E. H. LAND 3,249,433

PROCESS FOR PREPARING A PHOTOSENSITIVE ELEMENT AND PROCESS OF USING SAME IN A DIFFUSION TRANSFER METHOD Filed Sept. 1, 1960 SUPPORT INTERNAL PHASE CONTAINING GAS FOR IMPARTING VISCOSITY EXTERNAL PHASE CONTAINING A PHOTOSENSITIVE MATERIAL SUPPORT FOAM SUPPORT V sILvER PRECIPITATING STRATUM I 20 I INTERNAL GASEOUS PHASE EXTERNAL PHASE CONTAINING FOAM sILvER HALIDE I2 XI SUPPORT F I G 2 SUPPORT INTERNAL GASEOUS PHASE }FOAM T EXTERNAL PHASE CONTAINING 26 A PHOTOSENSITIZING MATERIAL 24 v PHOTOSENSITIVE STRATUM 22 SUPPORT FIG?) .z/IN VEN TOR.

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United States Patent 3,249,433 PROCESS FOR PREPARING A PHOTOSENSETIVE ELEMENT AND PROCESS OF USING SAME IN A DIFFUSION TRANSFER METHOD Edwin H. Land, Cambridge, Mass, assignor to Polaroid Corporation, Cambridge, Mass, a corporationof Delaware Filed Sept. 1, 1960, Ser. No. 53,541 5 Claims. (CI. 96-29) This application is a continuation-in-part of application Serial No. 635,501, filed January 22, 1957, now US. Patent 3,113,866, which, in turn is a continuation-impart of application Serial No. 500,073, filed April 8, 1955, now abandoned.

The present invention relates to photography and, more particularly, to the application of photographic foam compositions in thin layers to photographic sheets.

The present invention contemplates compositions which are characterized by dispersed gaseous bubbles. The gaseous bubbles provide, in the strict chemicalphysical sense, a foam or a froth, i.e., a dispersion having a liquid external phase and a gaseous internal phase. The term external phase or continuous phase is synonymous with such terms as dispersion medium and dispersion phase. The term internal phase or discontinuous phase is synonymous with such terms as dispersed medium and dispersed phase. Here, as in the case of foams in general, stable heterogeneous equilibrium between the external phase and the internal phase ordinarily requires the presence of one of the variety of materials known as foaming agents.

Foams of the present invention have been found advantageous for various reasons. For example, since interference by the internal phase with the mobility of agents in the external phase is small, interference with the agents activity is minimized; the dispersion retains a constant viscosity; the dispersion possesses a low thermal coefficient of viscosity, i.e., retains substantially a predetermined viscosity throughout a wide temperature range; the wetting characteristics of the external phase are substantially unaffected by the internal phase; and the dispersion possesses low coefficient of plasticity, i.e., flows immediately in response to applied forces.

Accordingly, the primary objects of the present invention are: to provide photographic processes in which foams are applied in thin layers to photographic strata, t-he foams being of the type comprising a liquid external phase that performs a photographic function and a gaseous internal phase, the external phase and the internal phase being initially isolated from each other; to provide photographic processes in which such foams are applied in thin layers to strata of the type employed in silver transfersreversal processes; and to provide compositions useful in the foregoing processes.

Other objects of the present invention are: to provide, as a novel photographic composition, a foam of the type comprising a liquid external phase including at least a photographic agent and a gaseous internal phase for rendering the composition relatively viscous; and to provide a novel photographic process in which a photographic composition of the foregoing type is applied, in a thin layer, to a photographic sheet.

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Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the composition possessing the features, properties and the relation of components and the process involving the several steps and the relation and order of one or more of such steps with respect to each ofthe others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

Generally, the external phase of a foam useful in a print-forming process of the present invention includes a relatively mobile aqueous solution or dispersion of a photographic agent. This agent may be a photosensitizing agent or a photosensitive material that is to be spread immediately before photoexposure is effected. Examples of suitable photosensitizing mate-rials are optical sensitizers and hyper-sensitizers. Examples of suitable photosensitive materials are photosensitive heavy metal salts, including silver salts and ferric salts, and diazonium compounds.

Generally, the internal phase of the foam includes a gas, preferably inert, such as nitrogen substantially insoluble in the external phase for imparting a relatively high viscosity to the foam. Spreading of the foam preferably is accomplished between a pair of sheets, the adjacent surfaces of one or both of which may be intended to participate in one or more photographic reactions. The sheets may be opaque or one or both of the sheets may be transparent so that photoexposure may occur after spreading, and viewing with or without stripping. The internal phase for .best results is contained in a quantity sufficient to impart to the foam a viscosity of from to 200,000 centipoises at a temperature of 20 C. This viscosity, which is high relative to that of the external phase itself, makes it possible to spread the foam uniformly and assures that it completely covers any area on which it is spread.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

FIGURE 1 illustrates, in distorted section, one embodiment of the present invention;

FIG. 2 illustrates, in distorted section, another embodiment of the present invention; and

FIG. 3 illustrates, in distorted section, still another embodiment of the invention.

With reference now to the drawing, wherein like numerals denote like parts, FIG. 1 illustrates a photosensitive foam 10 spread between the superposed surfaces of a sheet 12 and a sheet 14. Here the foam comprises a liquid external phase containing a photosensitive material such as, for example, a photosensitive silver halide salt or ferric salt or diazonium salt, and an internal phase containing nitrogen or another gas or mixture of gases substantively insoluble in the external phase. The foam also includes the presence of a suitable foaming agent. foaming agents for maintaining the external and internal phases of foam 10 in heterogeneous equilibrium are: fatty acids and fatty acid derivatives such as oleic acid and sodium oleate; saponins such as saponin; and hydrophilic amorphous materials such as gums including gum arabic, and proteins including gelatin. The internal phase Examples of of the foam is magnified for clarity in relation to the thickness of the layer of foam.

At least one of sheets 12 and 14 may be composed of a suitable material which is adapted to absorb or imbibe the external phase of the foam and, if desired, to bond the photosensitive material thereto. Sheets 12 and 14 may be composed of a paper and at least one surface thereof may be sized with a suitable material such as hardened gelatin or baryta in plastic. Alternatively, the supports may be composed of a plastic material which may be transparent, for example, cellulose nitrate, or an organic cellulose ester such as cellulose acetate, cellulose triacetate, cellulose propionate, cellulose butyrate, .or cellulose acetate butyrate. The interface between one of said sheets, for example, sheet 12 and foam 10, in order to assure good adhesion between it and the foam coating 10 containing in its extreme phase, for instance, a photosensitive silver halide salt, is treated, for example, with a mixture of gelatin and cellulose nitrate.

In one form, foam 10 contains in its external phase an aqueous dispersion of a ripened photosensitive silver halide salt, such as one or more of the silver halides, of which silver chloride, silver bromide and silver iodide are examples. In another form, foam 10 contains in its external phase an aqueous solution or dispersion of a photosensitive ferric salt which, when photoexposed, is capable of being reduced to a ferrous salt or a photosensitive diazonium compound. Here, one of the sheets 12 and 14 may be composed of a suitable paper the surface of which is adapted to absorb theexternal phase of the foam. Or one of the sheets 12 and 14 may be composed of or coated with a suitable colloid material which is adapted to imbibe the external phases of the foam. The photosensitive material may be photoexposed either before or after a processing composition therefor is spread in contact therewith.

FIG. 2 illustrates a photosensitive silver halide foam 16 spread between the superposed surfaces of a sheet 12 and a sheet 14 which includes a support 18 and a silver precipitating stratum 20. Foam 10 includes a liquid external phase containing a photosensitive silver halide salt and an internal phase containing a gas such as nitrogen which is insoluble in the external phase. The internal phase is magnified for clarity in relation to the thickness of the layer of foam 16. The silver halide salt may be photoexposed either before or after -a processing composition useful for forming a diffusion transfer print is contacted therewith. Once the silver halide salt is photoexposed and a processing composition spread or contacted with the photoexposed salt, the silver halide developer in the processing composition reduces exposed silver halide to silver and the silver halide solvent in the processing composition reacts with unreduced silver halide to form a complex silver'salt which dilfuses to stratum 20 where it is converted to silver to form a positive print. Thereafter, sheet 12,,together with the layer of foam 16, is stripped from sheet 14 to render the positive print available for use. Alternatively, as disclosed in U.S. Patent 2,861,885 issued to Edwin H. Land, where the covering power of silver in stratum 20 is much greater than the covering power of silver in layer 16, the composite print, which includes both the negative of layer 16 and the positive of stratum 20, is useful without stripping. In the latter case, the layer of foam 16 is dried to form a firm bond between the sheets.

It is to be under-stood that the processing composition need not effect silver transfer reversal but rather may merely developthe latent image formed in silver halide salt. In this case, sheet 14 is not provided with a silver precipitating stratum 20 and :serves merely to confine the foam during spreading and, where desired, to separate it from layer 16 during stripping.

Preferably silver precipitating stratum 20 is thin relative to silver halide foam stratum 16 and provides one of the vigorous silver precipitating environments de- 4 scribed in Patents Nos. 2,698,237 and 2,698,245, issued to Edwin H. Land on December 28, 1954. Such an environment includes silver precipitating nuclei such as the metal sulfides and selenides, the colloidal noble metals, or organic thio compounds dispersed in a macroscopically continuous vehicle comprising minute, preferably colloidal, particles of a water-soluble, inorganic, preferably siliceous, material such as silica aerogel. The positive print is formed in this stratum from fine silver particles concentrated primarily at its surface. Only a minute amount of silver in this condition is necessary for image formation because of its extremely high covering power.

Suitable silver halide developers for use in the process ing composition are benzene derivatives having at least two hydroxyl and/or amino groups substituted in ortho or para position on the benzene nucleus. Examples of such developers are hydroquinone, amidol, metol, glycin, p-aminophenol and pyrogallol. Developers of another type are hydroxylamines, in particular primary and secondary aliphatic and aromatic N'-substituted or B-hydroxylamines, which are soluble in aqueous alkali. Examples of such developers are hydroxylamine, N- methyl hydroxylamine, N-ethyl hydroxylamine, and others described in U.S. Patent No. 2,857,276. Examples of silver halide solvents useful in silver halide processing compositions for diffusion transfer processes are conventional fixing agents such as sodium thiosulfate, sodium thiocyanate, ammonium thiosulfate, ammonia and others described in the aforementioned Patent No. 2,543,181, and associations of cyclic imides and nitrogenous bases such as associations of barbiturates or uracils and ammonia or amines, and other associations described in U.S. Patent No. 2,857,274.

The foam may be carried by a container which, when deformed by opposed compressional forces, is capable of releasing its contents through a rupturable mouth. Such a container, as disclosed in the aforementioned U.S. Letters Patent No. 2,543,181, is constructed from a blank of three-ply sheet material having a single fold. The outer ply, serving as a backing or support, is composed of a thin, relatively inexpensive, tough material, preferably a paper such as kraft paper. The intermediate ply is composed of a substantially 'vapor-, liquid-impervious material, for example a metal foil such as'silver or lead. The inner ply is composed of a suitable thermoplastic or thermosetting plastic material, for example a polyvinyl acetal suchas polyvinyl butyral or polyvinyl formal, which protects the container contents from contamination. A composition comprising by weight approximately 60% to 70% polyvinyl butyral, approximately 20% to 23% of nitrocellulose and approximately 5% dibutyl sebacate is particularly satisfactory. At opposite end portions of each container, the two folds of the inner ply are sealed to each other as by the application of heat and pressure. Those sections of the two folds defining the mouth are bonded together by a strip of adhesive which is so constituted that the adhesive forces between the strip and the inner ply are less than the cohesive forces between end portions of the inner ply that are sealed together. A satisfactory strip may be composed, for example, of

ethyl cellulose or a mixture of ethyl cellulose and paraffin,

the mixture including at least 50% by weight of ethyl cellulose. Since the bonding forces between those sections defining the month are less than the bonding forces between the. other sections of the container, the application of opposed compressional forces to the container causes discharge of its contents through its mouth.

In a further form, shown in FIG. 3, sheet 12 includes a support 22 and a stratum 24 which contains a photosensitive salt, for example one or more of the silver halides, and foam 26 contains, in its external phase, a hypersensitizer or optical sensitizer. Foam 26 is spread upon the face of photosensitive stratum 24 with the aid of an auxiliary sheet 14 that serves merely to confine the foam during spreading and to separate it from sheet 12 during stripping. The internal phase is magnified for clarity in relation to the thickness of the layer of foam 26. For example, where the photosensitive material is a conventional gelatino silver halide dispersion, the external phase, in one form, contains an optical sensitizer such as a dye in extremely weak concentration. Suitable dyes include derivatives of fiuorescein such as erythrosine and eosin, and various cyanines such as thiazole, thiazoline, pyridine, benzoxazole, benzoselenazole, 3,3-dimethyl indolenine, naphtho (2,1) thiazole and naphtho (1,2) thiazole. Further examples of specific formulations of conventional optical sensitizing compositions suitable for use in an emulsion of the foregoing type are described in T. T. Baker, Photographic Emulsion Technique, American Photographic Publishing Company, Boston, 1948, Chapter IV.

Also, where the photosensitive material is a conventional gelatino silver halide dispersion, the external phase, in one form, contains a hypersensitizing composition. Such a hypersensitizing composition, for example, includes any one of ammonia, a thiourea such as palmityl thiourea or styrene funaryl allyl thiourea, allyl isocyanate, thiazole, quinolene and pyridine. Further examples of specific formulations of conventional hypersensitizing compositions suitable for such use are more fully described in Baker, supra, Chapter XV.

Stratum 24 may contain a photosensitive silver halide emulsion in which one or more of the silver halides, e.g., silver chloride, silver bromide and silver iodide, are dispersed in a suitable colloid material such as gelatin, casein, collod-ion, a cellulose ester, 2. polyvinyl alcohol, or a linear polyamide. Examples of specific formulations of conventional emulsions of the foregoing type are described in Baker, supra, Chapter IV.

In one form stratum 24 comprises a suitable photosensitive ferric salt, such as for example, ferric chloride, and ferric citrate. Suitable couplers for such ferric salts, for example, are potassium ferricyanide, potassium ferrocyanide, the tannins, fi-naphthaquinone sulfonic acid, and silver, platinum and palladium salts. Examples of specific formulations of conventional ferric and ferrous photosensitive and processing materials are described in Baker, supra, pages 268-275.

In another form stratum 24 comprises a suitable diazonium compound prepared, for example, by treating aromatic amines with nitrous acid at low temperatures. Suitable couplers for such diazonium compounds are phenols, naphthols and amino compounds that combine with exposed or unexposed diazonium compounds to form visibly distinguishable azo dyes. Examples of specific formulations of conventional diazonium photosensitive and processing materials are given in Baker, supra, pages 277-278, in L. P. Clerc, Photography, Theory and Practice, Pitman,'New York, 1937, page 444, and in J. S. Friedman, History of Color Photography, American Publishing Company, Boston, 1944, pages 487-493.

Alternatively, stratum 24 may be composed of a material capable, after being treated with a suitable dichromate solution, of becoming dilferentially insolubilized or tanned when photoexposed. The various regions of such a differentially insoluble coating are capable of forming a visible print by differentially absorbing a suitable color material. Here, stratum 24, for example, is a hydrophilic colloid material such as gelatin, glue or gum arabic, and foam 16 contains, in its external phase, a dichromate such as chrome alum, potassium dichromate or ammonium dichromate. Examples of specific formulations of conventional dichromate materials suitable for such use are described in Clerc, supra, pages 434-437 and page 419, Section 645.

It is recognized in the art that many a photographic composition, once coated on or otherwise applied to the surface of a sheet intended to be photoexposed, has a short useful life. For example, certain photosensitive compositions, oncecoated on the surface of a support sheet, are relatively unstable. Similarly, once applied, many compositions intended to hypersensitize or to optically sensitize photosensitive coatings are able to effectively perform their respective functions only for a short period. Furthermore, many photosensitive coatings are mixtures of distinct components intended to react with each other only when photoexp osed but nevertheless tending to react with each other though not photoexposed. The present invention thus contemplates a novel process comprising the spreading of a novel ph'otographic composition selected from the group consisting of the photosensitive silver, ferric, diazonium and chromate compounds, the optical sensitizing agents and the hypersensitizing agents between superposed surfaces of a pair of superposed sheets just prior to photoexposure.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A process for preparing a photosensitive element for use in recording visible records comprising the step of applying to a stratum containing a light-sensitive silver halide emulsion a relatively unstable silver halide optical sensitizing agent as a thin, substantially uniform layer of foam having substantially constant viscosity throughout a wide temperature range, said foam comprising a continuous liquid external phase containing said sensitizing agent and a discontinuous internal phase consisting essentially of an inert gas which is substantially insoluble in said external phase, said foam further including a foaming agent, said layer of said foam being applied to said stratum prior to utilization thereof in an apparatus to record a visible record by photoexposure.

2. A process for preparing a photosensitive element for use in recording visible records comprising the step of applying to a stratum containing a light-sensitive silver halide emulsion a relatively unstable silver halide hypersensitizing agent as a thin, substantially uniform layer of foam having substantially constant viscosity throughout a Wide temperature range, said foam comprising a continuous liquid external phase containing said hypersensitizing agent and a discontinuous internal phase consisting essentially of an inert gas which is substantially insoluble in said external phase, said foam further including a foaming agent, said layer of said foam being applied to said stratum prior to utilization thereof in an apparatus to record a visible record by photoexposure.

3. In a diffusion transfer process for preparing visible images wherein a photosensitive element containing a light-sensitive material selected from the group consisting of silver halide salts, ferric salts and diazonium salts in a layer on a support is photoexposed in a camera and a processing composition is spread between said exposed photosensitive element and a superposed image-receiving element to impart to said image-receiving element a visible image; the improvement which comprises applying said light-sensitive material to said support as a thin, substantially uniform layer of foam comprising a continuous liquid external phase containing said photographic material and a discontinuous internal phase consisting es- .sentially of an inert gas which is substantially insoluble in said external phase, said foam further including a foaming agent, said layer of said foam being applied to said support shortly before photoexposure thereof, and absorbing the external phase of said foam on the surface of said support.

4. A process as defined in claim 3 wherein said lightsensitive material is a photosensitive silver halide salt.

5. A process as defined in claim 3 wherein said inert gas in said discontinuous internal phase is of sufficient 7 8 quantity to impart to said foam a viscosity of from 100 3,020,155 2/ 1962 Yackel etal 9629 to 200,000 centipoises at a temperature of 20 C. 3,030,207 4/1962 Land 9629 3,087,816 4/1963 Land 9629 References Cited by the Examin 3,113,866 12/ 1963 Land 9629 UNITED STATES PATENTS v FO P ATENTS,

5/1919 Wall 413,178 7/1934 Great Britain. 2413?; 636,885 5/1950 Great Britain.

, 0 0e a 2/1951 Baldsiefen 96108 OTHER REFERENCES 4/1958 Knox et a1 9629 Meg'gers et al.,' J. Opt. Soc. Amer., vol. 4, pp. 91-104 11/1958 Tregillus 9629 XR (1920).

4/1959 Yutzy et a1. 9629 6/ 1960 Gray 96 94 NORMAN G. TORCHIN,-Primary Examiner. 7/ 1961 9629 15 PHILLIP E. MANGAN, Examiner. 1/1962 Harnman 9694 

1. A PROCESS FOR PREPARING A PHOTOSENSITIVE ELEMENT FOR USE IN RECORDING VISIBLE RECORDS COMPRISING THE STEP OF APPLYING TO A STRATUM CONTAINING A LIGHT-SENSITIVE SILVER HALIDE EMULSION A RELATIVELY UNSTABLE SILVER HALIDE OPTICAL SENSITIZING AGENT AS A THIN, SUBSTANTIALLY UNIFORM LAYER OF FOAM HAVING SUBSTANTIALLY CONSTANT VISCOSITY THROUGHOUT A WIDE TEMPERATURE RANGE, SAID FOAM COMPRISING A CONTINUOUS LIQUID EXTERNAL PHASE CONTAINING SAID SENSITIZING AGENT AND A DISCONTINUOUS INTERNAL PHASE CONSISTING ESSENTIALLY OF AN INERT GAS WHICH IS SUBSTANTIALLY INSOLUBLE IN SAID EXTERNAL PHASE, SAID FOAM FURTHER INCLUDING A FOAMING AGENT, SAID LAYER OF SAID FORM BEING APPLIED TO SAID STRATUM PRIOR TO UTILIZATION THEREOF IN AN APPARATUS TO RECORD A VISIBLE RECORD BY PHOTOEXPOSURE. 